1. Field of the Invention
The invention generally relates to a multi-component compartmentalized or zoned thermoplastic chip or pellet that provides a composition with a slower crystallization half time than homogenously dispersed chip of the same intrinsic viscosity. Said chip is useful in injection molding processes.
2. Related Art
In the injection molding process, polymer is injected into the mold with the thickest part usually being where the material is injected into the mold, called the tip. Because this tip will crystallize first, the part must be held into the mold long enough to cool it down to avoid crystallinity in the tip. If the polymer crystallizes slower, the part may be removed from the mold earlier, thus reducing the cycle time and improving the economics of the molding operation.
It is also advantageous to combine materials, such as postconsumer recycle polyester and virgin polyester, into one chip. However, when this is done as a homogeneous blend, the resulting polymer has a much faster crystallization rate (or lower crystallization half time). This increased rate of crystallinity lengthens the injection molding cycle time.
There is also the need for a way to combine two materials and achieve a more even Intrinsic Viscosity (I.V.) distribution, or reduced I.V. gradient, from the pellet's surface to the core. The advantages of more even I.V. distribution are described in United States Patent Application 2005/0196566, the teachings of which are incorporated by reference. The key advantages to having a more even IV distribution across the chip are less drop in molecular weight during extrusion and reduced energy consumption.
However, United States Patent Application 2005/0196566 achieves this by extruding a melt product having an Intrinsic Viscosity of 0.70 (dl/g) and then slightly increasing the I.V. via solid phase polymerization. While United States Patent Application 2005/0196566 contemplates the use of recycled polyester, it mentions nothing of combining it in the zoned or compartmentalized pellet structure.
There exists, therefore, the need to combine two similar polymers in a manner which can achieve a slower crystallization rate and provides the benefits of having a reduced I.V. gradient from the core to the surface.